Imaging capability of Laue lenses made of bent crystals for gamma-ray astrophysics telescopes

Forthcoming hard X-ray (50-700 keV) telescopes designed for high-energy astrophysics will rely on concentrating radiation through diffractive systems utilizing crystals and solid-state detectors at focal plane. Our current focus involves exploring the feasibility of employing Laue lenses, made from Germanium and Silicon bent crystals with curvature fitting the lens curvature. In this study, we simulate the diffraction patterns of an X-ray Laue lens made of bent crystals arranged in concentric rings on a disk of 2.5 m in diameter when incident X-rays arrive on- and off-axis on the lens. In each ring the crystals are oriented in order to diffract an X-ray beam to a focus plane positioned at 20 m from the lens. Each crystal is a tile 3x1 cm2, with the longer edge oriented toward the center of the lens. The 40 m curvature of each crystal permits to diffract a spot 1.5x10 mm2 in size at the focus plane. While an on-axis X-ray beam is focused on the focus plane with a 40 arcsec point spread function, off-axis X-ray beams produce rings of diffraction rings on the focal plane centered on the lens axis, thus confirming the poor imaging performance of the Laue lens. Nevertheless, using the Richardson–Lucy algorithm to deconvolute the diffraction pattern produced by off-axis X-ray beams permitted to improve the resolution in the an X-ray reconstructed image. This method has then been applied to a set of simulated X-ray sources with different off-axis values, assuming an increasing noise level as the background, confirming the imaging capability of Laue lens for hard X-ray sources.